I am just in the midst of designing a deck I can put over the boat when trailering so I can take the following: 2 - Dirt Bikes 1 - ATV 3 - Mountain Bikes Some camping gear.

My trailer is tandem axle with 3700lbs rating each.

My boat is 3000lbs. So I am assuming as long as I have the weight centered over the axles that I should be okay with an additional 1200lbs.

My idea is to build a light weight (frame with mesh)deck. That can be easily lifted by two people. Back mounts will slid onto boat guides and I will make similar boat guide posts in front of the axles... Quick release pins... and some long ramps.

Then when I go camping... I can take the camper... and all the toys...

To avoid modifying the trailer... I will use u-bolts etc... to add the new boat guide mounts.

Visually... it looks like it will work no problem... since the atv/dirt bikes will be sitting directly over the axles.

I would love to do something like in the picture.. but the wakeboard tower is the issue.

When I was originally in the market for a boat I saw a Malibu with an overhead bunk for a sit down jet ski. I think one thing to take into consideration would be the height of a standard overpass and such. Good luck with the project. Make sure to post some pics of it.